It’s a long shot, but I think what if the tvdb_ids should map to episodes?
could you try importing just one line, with tvdb_id 7152184?
That maps to the first episode of Vinland Saga.
https://www.thetvdb.com/series/vinland-saga/episodes/7152184
Then the “mistake” is trying to import at series level instead of episode level.
though I still wonder how Trakt can tell if you want to import a movie or a series for tmdb, or is each ID unique… questions of life hahahah